Page:Popular Science Monthly Volume 59.djvu/85

father, carries the young with her. In the Brazilian tree-frog (Hyla Goeldii), it is again the mother who bears the young with her. The eggs are very large and whitish and crowded together into a rounded mass on the back of the female, as represented in Fig. 9. While all the other frogs as yet mentioned seem to have no special organ or apparatus for holding the eggs or tadpoles as they carry them about with them, this Brazilian frog is provided with a growth of skin on its back to form a wall all around the eggs so that they lie in a spoon-like depression. The knowledge of such a change in the skin of the back for egg carrying may make us more ready to receive the accounts of the Surrinam toad described by Mile. Merrain in 1705. When, in 1725, the Dutchman Ruysch described the remarkable pits for carrying young which this creature has upon its back, the account met with natural skepticism, but at the present day reiterated observations place

Fig. 9.

Fig. 10.

the main facts beyond doubt. The female of this toad (Pipa dorsigera), as seen in Fig. 10, bears its young upon its back, each in a separate case, like so many papooses.

The cases are made at the breeding season, and before that the two sexes look alike. How the eggs get into these special receptacles is still an unanswered question, though the male may be a factor in the case; at all events, when the male goes away after being some twenty-four hours on the back of the female, the spawn is found on the back of the female, where the eggs gradually sink down into circular pits, that are hollowed out in the skin, and are 10-15 mm. deep. When an egg has sunk down into one of these pits, a thick, leathery or horny roof forms over it, and thus shuts it out from the external world.

These roofs are 5-6 mm. thick, and have a dark color unlike the rest of the back. Whether they, like the rest of the chamber about the egg, are formed from the skin, or whether they may be modified rem-